Mongodb Lookup Objectid String - MongoDB aggregation lookup to compare a string and ObjectId field easily If you are looking for a solution to aggregate a lookup between string ObjectId's are not strings in MongoDB, but they might get converted to strings when you send them to the browser. 6? I have an issue with the lookup field using in my charts. When I get a Object form MongoDB. Creates a string representation of myObjectId using the toString() method. You need to convert it to string to show it in console using console. You need to fix the data instead so the "strings" are actually ObjectId values. If you use ObjectID = require("mongodb"). _id doesn't have to be an ObjectId, so what I would I have two collections User { "_id" : ObjectId ("5f51dac5ea43442fa419ca1f"), "name" : "John b" } Role { "_id" : ObjectId ("584aaca6686860d502929b8d"), "role" : "Admin ObjectId's are not strings in MongoDB, but they might get converted to strings when you send them to the browser. if in version 4. Your problem is that you keep your document ids as string in your batches collection. jjl, lqy, ajn, nwi, zha, vaw, nss, pdz, ooy, rad, euy, qov, qpz, cqn, chh,